Spindle gear for an adjusting device in a motor vehicle seat

ABSTRACT

A spindle gear for a motor vehicle seat adjusting device having a housing, a spindle nut, a spindle and a worm wheel. The spindle nut may have an external bearing surface and a bearing shell may include an internal bearing surface cooperating with the external bearing surface. The spindle nut may have a slide lacquer coat. The spindle nut may have an external bearing surface and a stop disk may be attached to the external bearing surface so as to surround it. A projection may engage a corresponding spindle nut recess. The housing may comprise at least two housing parts made of zinc diecasting. The external teeth of the spindle nut may form a globoidal gear. The external spindle nut teeth may have an outer diameter that is smallest in an axial center thereof and increases toward the axial end regions.

[0001] The invention relates to a spindle gear for an adjusting devicein a motor vehicle seat, more specifically for a lengthwise adjustmentdevice of a motor vehicle seat. The spindle gear has a housing, aspindle nut, which is rotatably carried within the housing, has aninternal thread matching a longitudinally extending thread of thespindle and is comprised of external teeth, and a worm wheel that isrotatably carried within the housing and is comprised of a worm thatmeshes with the external teeth of the spindle nut.

[0002] Spindle gears are successfully utilized in motorized vehicleseats. They more specifically serve to longitudinally adjust the motorvehicle seat but may as well be utilized for performing other adjustmenttasks such as reclining adjustment of the seat back, vertical adjustmentof the seat, and so on. The drive thereby uses an electric motor.Electric motors operate at quite high RPM, the spindle gear permittingto achieve a very considerable gear reduction ratio for each line unit.The gear reduction thereby occurs in two stages. The worm wheel rotatesat a RPM speed that corresponds to the speed of the electric motor. Afirst transmission is achieved by the worm gear between the worm wheeland the external teeth of the spindle nut. In the second transmissionstage mating occurs between spindle nut and spindle, the latter beingprovided with a screw thread.

[0003] The spindle thread must be capable of transmitting a certaintorque. If used in a lengthwise adjustment device, the torquetransmitted must be high enough to suffice for the movement of a personsitting on the motor vehicle seat. The noise level must thereby remainlow. A change in the direction of rotation occurring for example duringswitching between fore and aft adjustment is not allowed to generate anoticeable noise. This must apply to all of the usually occurring seatloads.

[0004] Finally, the spindle gear must also be capable of taking impactforces as they occur for example in a frontal crash of a motor vehicle.Together with the spindle, the spindle gear secures the longitudinalposition of the motor vehicle seat. Here, sufficient provisions must bemade to prevent crash acceleration from leading to unwanted adjustmentof the motor vehicle seat.

[0005] Numerous embodiments of spindle gears have been previously knownin the art and the reader is referred, by way of example only, to thefollowing documents WO 86-06036 A; DE 41 001 470 C; DE 1755740 A; U.S.Pat. No. 6,260,922 B1; U.S. Pat. No. 5,222,402 and U.S. Pat. No.5,349,878.

[0006] In view of these spindle gears, it is the object of the inventionto indicate a particularly smooth running spindle gear that,accordingly, makes little operating noise under all operatingconditions.

[0007] In view of the spindle gear of the type mentioned herein above,the solution to this object is achieved in that at least one, preferablyseveral or all, of the following features are met:

[0008] that the spindle nut comprises at least one external bearingsurface that is axially offset relative to the external teeth, that abearing shell is provided that comprises an internal bearing surfacecooperating with the external bearing surface, that the bearing shellcomprises an axial slot and that the bearing shell is inserted withinthe housing so as to be secured against torsion and/or

[0009] that the spindle nut comprises a slide lacquer coat, said coatbeing provided on the external teeth and/or on the internal threadand/or

[0010] that the spindle nut comprises at least one external bearingsurface that is axially offset relative to the external teeth, that astop disk is provided that is placed onto said external bearing surfaceso as to surround it, that the stop disk has a projection (e.g., anaxial one) that engages into a corresponding recess of the spindle nut,more specifically between two teeth of the external teeth of the spindlenut, and forms an antirotation lock and/or

[0011] that the spindle nut comprises at least one external bearingsurface that is axially offset relative to the external teeth, that astop disk is provided that is attached to said external bearing surfaceso as to surround it and that the stop disk comprises a slide lacquercoat and/or

[0012] that the housing is composed of at least two housing parts thatare made of zinc diecasting and/or

[0013] that the external teeth of the spindle nut are a globoidal wormgear and/or

[0014] that the external teeth of the spindle nut have an outer diameterthat is smallest in the region of the axial center thereof and thatincreases toward the axial end regions, more specifically in the form ofa curve.

[0015] It has been found that each of these features is advantageous forreducing the operating noise of the spindle gear around its mountinglocation within the vehicle seat. Preferably, all of the featuresmentioned are implemented although merely providing the spindle gearwith some of the features already proved advantageous as well. The mereuse of but one of the features indicated already detectably reduces theoperating noise.

[0016] The various features mentioned will be discussed herein after:

[0017] Usually, bearing shells are configured to be annular; now, it issuggested that the bearing shell be provided with a slot that is forexample oriented radially. Two end faces that are separated by an airgap are thus formed. Said air gap may vary during operation. Thisvariation permits to compensate for mechanical deviations duringrotation. The material of the bearing shell preferably has elasticproperties, a metal is used for example.

[0018] Coating the spindle nut with a slide lacquer permits on the oneside to reduce friction between spindle nut and longitudinal thread ofthe spindle and on the other side to lower the noise level. The termslide lacquer coat is to be construed herein as any lacquer coating suchas MoS₂ anti-friction films, MoS₂ lacquers or plastics such aspolytetrafluor ethylene (PTFE) or similar polymers.

[0019] Locking rotation of the stop disk relative to the spindle nutnoticeably lowers the noise level. Now, the stop disk is no longer aplain washer that somehow moves more or less together with the nut, itnow rotates together with the spindle nut. The locking of the stop isachieved by an axial projection protruding from the stop disk andcooperating with the spindle nut, preferably engaging betweenneighboring teeth. Thus, the mechanical expense for locking rotation isextremely low. Kinematic inversion is also possible, the spindle nutbeing provided, for this very purpose, with the projection and the stopdisk with a mating recess.

[0020] Coating the stop disk, meaning more specifically the two radiallyoriented surfaces, with a slide lacquer coat, leads to an operatingnoise reduction.

[0021] Basically, housings that are composed of two or more housingparts are known. For reducing the operating noise by constructionaldesign, a housing made of zinc diecasting has proved efficient; itconstitutes an advantageous combination, in particular in combinationwith the other features.

[0022] The globoidal engagement of the external teeth of the spindle nutresults in an advantageous smooth meshing and reduces the operatingnoise.

[0023] As compared to a mere axial shape, the curved shape of thespindle nut as viewed in axial section increases the surfaces of contactwith the worm thread of the worm wheel.

[0024] The applicant reserves the right to claim each and every of thefeatures a)-g) mentioned and any combination thereof.

[0025] Further embodiments of the invention are recited in thesubordinate claims, with only some of them being discussed herein after.

[0026] Further, it has been found advantageous to non-rotatably disposethe bearing shell relative to the housing. For this purpose, the bearingshell has a lug that projects radially and/or axially, the housinghaving a mating recess. Kinematic inversion is also possible, with, inthis case, the housing having the lug and the recess being provided inthe bearing shell. Preferably, the lug is thereby disposed diametricallyopposite the slot of the bearing shell. As a result thereof, themobility of the bearing shell in the region of the slot is leastaffected by the antirotation lock.

[0027] Eventually, it is advantageous to configure the curved shape ofthe external teeth in such a manner that a substantially axiallyoriented, short central contour line is provided. Said central contourline is then adjoined on either side with a curved contour line. Thisallows for compensating the tolerances, which again aids in reducing thenoise.

[0028] Further advantages and characteristics of the invention willbecome more apparent upon reading the following non restrictivedescription of an exemplary embodiment thereof, given with reference tothe drawing in which:

[0029]FIG. 1 is an exploded assembly drawing of a spindle gear,

[0030]FIG. 2 is a perspective view of the bearing shell as shown in FIG.1 and

[0031]FIG. 3 is an axial section through a worm wheel shown in amodified configuration with respect to FIG. 1.

[0032] The spindle gear has a housing that is composed of a firsthousing part 20 and of a second housing part 22. The two parts are madeof zinc diecasting. The two parts 20, 22 are joined together byriveting. The housing 20, 22 forms an inner volume and bearing regionsfor a spindle nut 24 on the one side and for a worm wheel 26 on theother side. In the axial direction, the housing 20, 22 is openthroughout for receiving a spindle 28 that is merely outlined herein. Ithas a longitudinal thread 30.

[0033] The spindle nut 24 has an internal thread 32 that meshes with thelongitudinal thread 30 of the spindle 28 and external teeth 34. In theimplementation shown in FIG. 1, the outer lines of the external teeth 34lie on a cylinder. On either side of the external teeth 34, an externalbearing surface 36 is formed, said external bearing surface beingcylindrical and having an outer diameter that is smaller than the outerdiameter of the external teeth 34 at the bottom of the spaces betweenthe teeth, meaning smaller than the dedendum circle of the teeth 34.

[0034] A flat stop disk 38 is attached to each external bearing surface36. It is coated with a slide lacquer, more specifically with PTFE onits two-main surfaces, preferably allover. It has a projection 40 which,in the embodiment shown, protrudes axially although it may as well beconfigured on a radial axis. In the assembled condition, said axialprojection 40 engages between two teeth of the external teeth 34, thusproviding an antirotation lock. Said lock may be provided with a certainclearance which may be adjusted by, for example, adjusting theprojection, for example its dimensions, in the circumferentialdirection.

[0035] Outside of each stop disk 38, a bearing shell 42 in turn forms agrip around a respective one of the external bearing surfaces 36. Ascompared to the axially relatively thin stop disk 38, the bearing shellhas an axial length in the range of several millimeters, e.g., of 3-6millimeters. In terms of facts, it consists of a ring that substantiallycorresponds to the ring of the stop disk and of a collar of a smallerouter diameter that is turned away from the external teeth 34. Together,these two portions form the inner bore. A lug 44 projects radially fromthe collar. On the diametrically opposite side thereof a slot 46 isformed so that the bearing shell 42, while being made from one piece, issubstantially implemented with the shape of a C. The slot is providedwith small dimensions ranging for example from 0.1 to 2 mm. It providesan air gap 46. In the embodiment shown, the slot is obtained by a cutthat is made in the radial and the axial direction. The air gap 48 maybe defined otherwise as well.

[0036] The bearing shell 42 is made from a metal that has advantageousslide properties relative to the metal from which the spindle nut 24 ismade. It is also possible to manufacture the spindle nut 24 fromreinforced plastics.

[0037] In the first housing part 20, bearing grooves 50 are provided forreceiving the outer edge of the bearing shell 42. The housing 20, 22also comprises a recess receiving the lug 24 so that the bearing shell42 is prevented from rotating relative to the housing 20, 22.

[0038] Further, the worm wheel 26 is carried within the housing 20, 22.Its axis substantially forms a right angle and is offset relative to theaxis of the worm wheel 26 and of the spindle 28. It has a worm 52 on itsouter case and within a polygonal seat for receiving an elastic driveshaft. At each axial end, the worm wheel 26 is rotatably carried on aball bearing 56 within the housing 20, 22. Bearing bushes 58 that aresimilar to the bearing shells 42 are additionally provided.

[0039]FIG. 3 shows an axial section through a spindle nut 24 that ismodified relative to the implementation shown in FIG. 1. The lines ofthe top lands of the external teeth 34 now no longer lie on a cylinderbut on a rotational body that bears certain similarity to a diabolo or ayarn reel. As shown in FIG. 3, the external teeth 34 have asubstantially axially oriented central contour line 60 that extends overa quite short axial distance of for example 0.5-3 mm, preferably of 1.5mm. It is oriented parallel to the axis of the spindle nut 34. On eitherside, said central contour line 60 is homogeneously and continuouslyadjoined with a curved contour line. As a result, the outer diameter ofthe external teeth 34 increases steadily, reaching its maximum in therespective border region of the external teeth 34. The contours 60, 62may be roughly described as a circle the diameter of which is greaterthan the outer diameter of the worm wheel 26. It preferably may be 1.5-3times the outer diameter of the worm wheel 26.

[0040] For silencing, two shells 64 made of rubber or of a correspondingmaterial straddle the gear in a manner well known in the art, said gearbeing accommodated in a substantially U-shaped bearing angle 64.

1. A spindle gear for an adjusting device in a motor vehicle seat, saidspindle gear comprising a spindle having a longitudinally extendingthread, housing, a spindle nut, which is arranged within the housing, isrotatable within the housing, has an internal thread matching the threadof the spindle and comprises external teeth, and a worm wheel that isarranged within the housing, is rotatable within the housing andcomprises of a worm gear that meshes with the external teeth of thespindle nut, wherein the spindle gear further comprises at least one ofthe following features a) to g): a) that the spindle nut comprises atleast one external bearing surface that is axially offset relative tothe external teeth, that a bearing shell is provided that comprises aninternal bearing surface cooperating with the external bearing surface,that the bearing shell comprises a slot and that the bearing shell isinserted within the housing so as to be secured against torsion; b) thatthe spindle nut comprises a slide lacquer coat, said slide lacquer coatbeing provided on at least one of the external teeth and on the internalthread; c) that the spindle nut comprises at least one external bearingsurface that is axially offset relative to the external teeth, that astop disk is provided that is attached to said external bearing surfaceso as to surround it, that the stop disk has a projection which engagesinto a corresponding recess of the spindle nut and forms an antirotationlock; d) that the spindle nut comprises at least one external bearingsurface that is axially offset relative to the external teeth, that astop disk is provided that is attached to said external bearing surfaceso as to surround it and that the stop disk comprises a slide lacquercoat; e) that the housing is composed of at least two housing parts thatare made of zinc diecasting; f) that the external teeth of the spindlenut are made as a globoidal gear; and g) that the external teeth of thespindle nut have an outer diameter that is smallest in the region of theaxial center thereof and that increases toward the axial end regionsthereof.
 2. The spindle gear according to claim 1, wherein the outerbearing surface of the spindle nut is cylindrical and two bearingsurfaces are provided, the external teeth being located between the twobearing surfaces.
 3. The spindle gear according to claim 1, wherein thebearing shell has an outer border and the housing forms a receivinggroove mating with said outer border.
 4. The spindle gear according toclaim 1, wherein the bearing shell forms a radially projecting lug andthe housing forms a recess for receiving said lug.
 5. The spindle gearaccording to claim 1, wherein the external teeth, as viewed in axialsection, have a substantially axially oriented central contour linehaving a right side and a left side, a left curved contour lineadjoining on the left side and a right curved contour line adjoining onthe right side, the axial length of the left curved contour line and theright curved contour line is greater than the axial length of thecentral contour line.
 6. The spindle gear according to claim 1, whereinthe spindle gear is for a lengthwise adjustment device of a motorvehicle seat.
 7. The spindle gear according to claim 1, wherein thespindle gear further comprises at least two of the features a) to g). 8.The spindle gear according to claim 1, wherein the spindle gear furthercomprises at least three of the features a) to g).
 9. The spindle gearaccording to claim 1, wherein the spindle gear further comprises atleast four of the features a) to g).
 10. The spindle gear according toclaim 1, wherein the spindle gear further comprises several of thefeatures a) to g).
 11. The spindle gear according to claim 1, whereinthe spindle gear further comprises all of the features a) to g).
 12. Thespindle gear according to claim 1, wherein the projection engagesbetween two neighboring teeth of the external teeth of the spindle nut.13. The spindle gear according to claim 1, wherein the outer diameterincreases from the axial center of the external teeth of the spindle nuttowards the axial regions of the external teeth in the form of a curve.